The present invention relates to a method for testing electrical modules.
Electrical modules must be tested before their release. On a known testing machine, which is referred to as the flying probe tester, the electrical modules to be tested are tested without supply voltage.
The flying probe tester comprises contacting elements for producing electrical contacts with contacting points of the electrical module to be tested. The contacting elements nearly xe2x80x9cflyxe2x80x9dxe2x80x94as the name of the testing machine already suggestsxe2x80x94back and forth over the electrical module under test and successively contact respectively prescribed groups of contact points on the electrical module under test in order to measure electrical quantities such as resistance, capacitance and inductance thereat. On the basis of the measured values and dependent on the location of the measured values, the test program then diagnoses short-circuits between line networks as well as components on the electrical module under test that are incorrect, not present at all or incorrectly contacted. The events described above sequence in what are referred to as short-circuit or component tests and are also often referred to in this way below.
Within the tests, the individual test types can be classified as indicated in the following enumeration:
1. Short-circuit test
2 Component test
3. Open test, i.e., test for missing components or incorrectly contacted components.
The test machine must execute what are referred to as motion steps for the tests. Motion steps are steps wherein the test machine brings the contacting elements to and contacts the groups of contacting points to be contacted on the electrical module under test. After the contacts have been produced, the test machine implements one or more testing steps in which it measures one or more of the aforementioned electrical quantities and interprets them dependent upon the location of the measurement.
Dependent on the type of electrical module, electrical modules can comprise 200 resistance, capacitance and inductance components on average and can have 500 line networks with which the components are connected to one another. A line network comprises both the lines to the individual components as connection element between the components as well as the components pins with all galvanically connected elements inside the component.
Further, the electrical modules can have line networks arranged on the electrical module such that, on average, one line network has respectively 5 neighboring networks to which a short can respectively occur.
In order to assure freedom from shorts in previous short-circuit and component testing methods, measurements are carried out between all line networks and respectively all line networks coming into consideration per line network for a short. The measurements for implementing the component test then follow. A separate motion step is executed for each measurement, particularly for each measurement in the short-circuit test phase. In terms of motion steps for the short-circuit and component test, this means
(500 LN) * (5 neighboring LN)=2,500 for short-circuit test
200 components=200 for element test,
LN denotes: line network,
with reference to the aforementioned example of a specific type of electrical module.
The motion steps to be accomplished by the flying probe tester therefore amount to 2,7000 motion steps.
The flying probe tester is not especially fast because of the mechanical movements of the contacting elements. Nonetheless, it is well-suited for electrical modules that are issued in small numbers of units in order to subject these to short-circuit and component tests. The flying probe tester can be programmed relatively fast and simply and is therefore valuable for this type of electrical module.
U.S. Pat. No. 5,006,808 discloses a testing method for unequipped modules wherein a flying probe tester is employed for testing. The main test of the module ensues via capacitance measurements between the individual line networks. When the measurements exhibit unanticipated values, supplementary resistance measurements are implemented. The known method does not enable the testing of arbitrarily equipped modules with comparatively few testing steps.
Japanese Patent Application No. 61 180 153 discloses a testing method for testing equipped modules. The testing, however, does not ensue with a flying probe tester. Moreover, the modules to be tested therein comprise only line networks that have measurable resistances. Capacitance and/or inductance measurements are not taken into consideration here. The document is therefore limited to testing resistor networks. A testing of arbitrarily equipped modules with comparatively few testing steps is also not possible with this document.
It is therefore an object of the present invention to reduce the number of motion steps in the short-circuit and component testing of arbitrarily equipped electrical modules while retaining the complete freedom from shorts.
The object is inventively achieved in accordance with the present invention in a method for testing modules.
In accordance therewith, a number of motion steps in the short-circuit test may be limited to the number of existing line networks. When no fault is discovered with these motion steps, the freedom from shorts may thus automatically be assured overall. The freedom from shorts was previously obtained only by measuring between all respectively neighboring line networks. A reason for the limitation to the handful of motion steps in the present method is the possibility of short-circuit statements on the basis of the electrical quantities obtained in the measurements at the respective, individual line networks with reference to an existing ground reference point or to a respectively pertaining reference potential. On the occasion of these measurements and without additional motion steps, moreover, components are co-tested to a certain extent either immediately or, on the other hand, with merely a further testing step having a slight additional measuring time, for example a test for a predetermined capacitance value in addition to a test for a predetermined resistance value. Respectively separate motion steps are thus needed for obtaining each of these items of information. These are only necessary in order to be able to diagnose the fault when particular constellations of faults are present. Since it can be assumed that a high degree of production quality prevails in a fabrication, such additional measurements are only rarely required. In the previous short-circuit testing method, additional measurements were a constituent part of the measurement program. The present inventive method of the short-circuit and component test also has the advantage that the testing time can be kept short in that an optimum path, i.e., a path that includes a shortest distance overall, can be adhered to in the processing of the individual measurements at the respective line networks referred to ground/potential.
In accordance therewith, supplementary testing steps with their respectively own motion steps can in fact be necessary in certain special fault instances. These, however, are limited to those line networks whereat the faults occurred. Only a few supplementary testing and motion steps therefore need be implemented.
The fact that the tests are always implemented with the same reference point (ground/potential) has the advantage that a single contacting element can be employed for respectively all tests in conjunction with this reference point. I.e., the contacting element allocated to this reference point can be kept at the reference point during the various measurements without a motion step.
The inherently known, simple methods of resistance, capacitance and inductance measurement suffice for the implementation of the individual testing tests, so that no added outlay for the measuring is required compared to that previously known.